1. Field of the Invention
The present invention relates to gas concentration detection sensors.
2. Description of the Related Art
To date, a gas concentration detection sensor that detects the concentration of a specified gas such as NOx or oxygen included in an object gas such as an exhaust gas from an automobile has been known. In this gas concentration detection sensor, the temperature of a sensor element may be decreased and cracking may occur due to, for example, adhesion of water generated when an engine is started to the sensor element, or a sudden increase in the flow rate of the object gas that strikes the sensor element. For this reason, a technology that prevents these disadvantages by mounting a protective cover that covers the sensor element has been proposed. For example, a gas concentration detection sensor described in Patent Document 1 is provided with a double-layered protector, which has a vent hole formed therein in order to introduce an exhaust gas into the sensor, along the outer circumference of the front end of the sensor element as a protective cover.